Worm gearboxes with countless combinations
Ever-Power offers a very wide self locking gearbox selection of worm gearboxes. Because of the modular design the typical programme comprises many combinations with regards to selection of equipment housings, mounting and connection options, flanges, shaft designs, kind of oil, surface solutions etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We simply use top quality components such as properties in cast iron, light weight aluminum and stainless, worms in the event hardened and polished steel and worm tires in high-grade bronze of particular alloys ensuring the the best wearability. The seals of the worm gearbox are provided with a dust lip which effectively resists dust and water. In addition, the gearboxes happen to be greased for life with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for reductions of up to 100:1 in one single step or 10.000:1 in a double reduction. An comparative gearing with the same gear ratios and the same transferred vitality is bigger when compared to a worm gearing. In the mean time, the worm gearbox is usually in a far more simple design.
A double reduction could be composed of 2 regular gearboxes or as a particular gearbox.
Compact design
Compact design is probably the key terms of the standard gearboxes of the Ever-Power-Series. Further optimisation can be achieved through the use of adapted gearboxes or particular gearboxes.
Low noise
Our worm gearboxes and actuators are really quiet. This is due to the very clean running of the worm gear combined with the utilization of cast iron and large precision on part manufacturing and assembly. In connection with our precision gearboxes, we take extra attention of any sound which can be interpreted as a murmur from the gear. So the general noise degree of our gearbox is reduced to a complete minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This frequently proves to become a decisive gain producing the incorporation of the gearbox considerably simpler and more compact.The worm gearbox is an angle gear. This can often be an advantage for incorporation into constructions.
Strong bearings in sturdy housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the gear house and is ideal for immediate suspension for wheels, movable arms and other areas rather than needing to create a separate suspension.
Self locking
For larger equipment ratios, Ever-Ability worm gearboxes will provide a self-locking impact, which in lots of situations can be used as brake or as extra protection. Also spindle gearboxes with a trapezoidal spindle will be self-locking, making them well suited for a broad range of solutions.
In most equipment drives, when driving torque is suddenly reduced consequently of electrical power off, torsional vibration, vitality outage, or any mechanical failing at the tranny input side, then gears will be rotating either in the same way driven by the machine inertia, or in the contrary direction driven by the resistant output load because of gravity, planting season load, etc. The latter state is known as backdriving. During inertial action or backdriving, the driven output shaft (load) becomes the generating one and the traveling input shaft (load) turns into the powered one. There are various gear drive applications where end result shaft driving is unwanted. As a way to prevent it, several types of brake or clutch units are used.
However, there are also solutions in the apparatus transmission that prevent inertial motion or backdriving using self-locking gears without any additional products. The most typical one is normally a worm gear with a low lead angle. In self-locking worm gears, torque applied from the strain side (worm equipment) is blocked, i.e. cannot drive the worm. Even so, their application comes with some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low velocity, low gear mesh proficiency, increased heat generation, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can utilize any gear ratio from 1:1 and larger. They have the generating mode and self-locking method, when the inertial or backdriving torque is definitely put on the output gear. Primarily these gears had suprisingly low ( <50 percent) driving efficiency that limited their request. Then it was proved [3] that great driving efficiency of these kinds of gears is possible. Criteria of the self-locking was analyzed in this posting [4]. This paper explains the basic principle of the self-locking process for the parallel axis gears with symmetric and asymmetric pearly whites profile, and reveals their suitability for diverse applications.
Self-Locking Condition
Figure 1 presents conventional gears (a) and self-locking gears (b), in the event of backdriving. Figure 2 presents conventional gears (a) and self-locking gears (b), in the event of inertial driving. Pretty much all conventional gear drives have the pitch stage P located in the active portion the contact line B1-B2 (Figure 1a and Physique 2a). This pitch level location provides low particular sliding velocities and friction, and, due to this fact, high driving efficiency. In case when this sort of gears are powered by productivity load or inertia, they will be rotating freely, because the friction instant (or torque) is not sufficient to stop rotation. In Figure 1 and Figure 2:
1- Driving pinion
2 – Driven gear
db1, db2 – base diameters
dp1, dp2 – pitch diameters
da1, da2 – outer diameters
T1 – driving pinion torque
T2 – driven gear torque
T’2 – driving torque, put on the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – driving force, when the backdriving or inertial torque applied to the gear
aw – operating transverse pressure angle
g – arctan(f) – friction angle
f – average friction coefficient
To make gears self-locking, the pitch point P ought to be located off the dynamic portion the contact line B1-B2. There will be two options. Choice 1: when the point P is placed between a middle of the pinion O1 and the idea B2, where in fact the outer diameter of the gear intersects the contact line. This makes the self-locking possible, but the driving efficiency will always be low under 50 percent [3]. Alternative 2 (figs 1b and 2b): when the point P is put between your point B1, where in fact the outer diameter of the pinion intersects the line contact and a center of the apparatus O2. This kind of gears can be self-locking with relatively excessive driving performance > 50 percent.
Another condition of self-locking is to have a ample friction angle g to deflect the force F’ beyond the center of the pinion O1. It creates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is usually a lever of the push F’1. This condition can be presented as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear amount of teeth,
– involute profile angle at the end of the apparatus tooth.
Design of Self-Locking Gears
Self-locking gears are custom. They cannot end up being fabricated with the specifications tooling with, for instance, the 20o pressure and rack. This makes them very ideal for Direct Gear Design® [5, 6] that provides required gear effectiveness and after that defines tooling parameters.
Direct Gear Design presents the symmetric equipment tooth created by two involutes of 1 base circle (Figure 3a). The asymmetric equipment tooth is shaped by two involutes of two numerous base circles (Figure 3b). The tooth tip circle da allows avoiding the pointed tooth idea. The equally spaced the teeth form the apparatus. The fillet profile between teeth was created independently in order to avoid interference and offer minimum bending tension. The working pressure angle aw and the speak to ratio ea are defined by the next formulae:
– for gears with symmetric teeth
(3) Equation 3
(4) Equation 4
– for gears with asymmetric teeth
(5) Equation 5
(6) Equation 6
(7) Equation 7
where:
inv(x) = tan x – x – involute function of the profile angle x (in radians).
Conditions (1) and (2) show that self-locking requires high pressure and substantial sliding friction in the tooth get in touch with. If the sliding friction coefficient f = 0.1 – 0.3, it requires the transverse operating pressure angle to aw = 75 – 85o. Consequently, the transverse contact ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse speak to ratio should be compensated by the axial (or face) contact ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This is often achieved by employing helical gears (Determine 4). Even so, helical gears apply the axial (thrust) power on the apparatus bearings. The double helical (or “herringbone”) gears (Shape 4) allow to pay this force.
Large transverse pressure angles bring about increased bearing radial load that may be up to four to five instances higher than for the conventional 20o pressure angle gears. Bearing selection and gearbox housing style should be done accordingly to carry this increased load without abnormal deflection.
Application of the asymmetric tooth for unidirectional drives allows for improved overall performance. For the self-locking gears that are being used to prevent backdriving, the same tooth flank is utilized for both driving and locking modes. In this instance asymmetric tooth profiles give much higher transverse contact ratio at the offered pressure angle compared to the symmetric tooth flanks. It makes it possible to lessen the helix angle and axial bearing load. For the self-locking gears that used to avoid inertial driving, numerous tooth flanks are being used for driving and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high efficiency for driving setting and the contrary high-pressure angle tooth profile is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical equipment prototype models were made predicated on the developed mathematical products. The gear info are provided in the Table 1, and the test gears are shown in Figure 5.
The schematic presentation of the test setup is shown in Figure 6. The 0.5Nm electric engine was used to drive the actuator. A swiftness and torque sensor was attached on the high-acceleration shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low rate shaft of the gearbox via coupling. The insight and productivity torque and speed details had been captured in the data acquisition tool and additional analyzed in a pc employing data analysis software. The instantaneous performance of the actuator was calculated and plotted for a broad range of speed/torque combination. Normal driving effectiveness of the personal- locking gear obtained during screening was above 85 percent. The self-locking home of the helical gear occur backdriving mode was likewise tested. In this test the external torque was put on the output equipment shaft and the angular transducer revealed no angular activity of source shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been used in textile industry [2]. However, this type of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial driving is not permissible. One of such software [7] of the self-locking gears for a continually variable valve lift program was suggested for an auto engine.
Summary
In this paper, a basic principle of work of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and screening of the apparatus prototypes has proved relatively high driving efficiency and reliable self-locking. The self-locking gears may find many applications in a variety of industries. For instance, in a control devices where position balance is vital (such as for example in motor vehicle, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to achieve required performance. Like the worm self-locking gears, the parallel axis self-locking gears are delicate to operating circumstances. The locking dependability is affected by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and requires comprehensive testing in every possible operating conditions.